Brake mechanism



Feb; 25, 1941 3 M. B. CAMERON BRAKE IECHANISK Fud llarph 51, 19:59 2 Sheets-Sheet 1 INVENTOR 'NIORTIMER B.CAMERON ATTORN E Y "Feb.25, 1941. a v 2,232,902

BRAKE MECHANISII Filed larch 51 1939 2 Sheets-Sheet 2 INVENTOR B MORTIMER a. CAMERON v I BY ATTORNEY Patented F eb. 25, 1941 BRAKE MECHANISM Mortimer B. Cameron, Edgewood, Pa., assignor to The Westinghouse Air Brake Company, Wil- .merding, Pat, a corporation of Pennsylvania Application March 31, 1939, Serial No. 265,209 1': Claims. (Cl. 188-56) This invention relatestobrake mechanism for railway vehicle trucks and more particularly to the general type disclosed in the pending application of Carlton D. Stewart. Serial No. 214,517, 5' filed June 18, 1938, which has become Patent No. 2,177,953, issued Oct. 31, 1939, which embodies a plurality of brake elements arranged in clasp relation at opposite sides of a rotatable member to be braked and one or morev additional brake 10 elements disposed above said member and cooperative with the clasp brake elements for braking said member.

In effecting an application of the brakes with the usual type of brakerizging embodying a brake element supported from the truck frame below the horizontal centerline of the truck wheel or other member to be braked, said brake element after engaging the wheel is forced downwardly along the tread of.- the wheel towards the track rail and acts to pull the frame downwardly in opposition to the usual frame supporting springs.

The degree of the downward movement Just described depends mainly upon the pressure applied to the brake element for forcing same into 5 braking engagement with the truck wheel, and where high braking pressures are employed, as in high speed train service, the truck frame may be pulled downwardly against its supporting springs, until it meets a solid stop.

This downward movement of the truck frame in applying the brakes is undesirable for various reasons, one of which is that the compressive force of the frame supporting springs materially interferes with a flexible or accurate control of 35 the release of the brakes on the truck, as will now be-described in detail.

High speed trains are. usually braked to as great a degree as possible and it is the usual practice to reduce brake cylinder pressure gradu- 40 ally in order to elfect a partial release of the brakes when the wheels on the truck have ,a tendency to slip on the track rails. It is very desirable that this partial release of the brakes be accomplished very quickly and with a mini- 45' mum reduction of brake cylinder pressure so as to maintain the maximum braking effort on the truck without danger of wheel slipping. This control of release of brakes'is not possible however on a truck provided with a brake rigging so which acts in eifecting an application of the brakes to draw the truck frame down against and thus compress the frame supporting springs,

since in attempting to effect a release of the brakes, said springs acting through the medium as of the truck frame and brake rigging, drag the brake elements upwardly along the tread of the wheel toward the horizontal center-line thereof and in so moving maintain the brake elements in heavy braking engagement with the wheel.

From this it will be seen that the action of the truck supporting springs offsets to a large extent a reduction in brake cylinder pressure until such time as the truck frame and thereby the brake elements are raised to substantially their normal position, at which time the action of said springs on the brake rigging is annulled and the partial release of the brakes is finally effected through a further reduction in brake cylinder pressure. From'this it will be seen that the truck frame supporting springs act to delay a partial release of the brakes and therefore render it necessary "to reduce brake cylinder pressure "much lower than desired, thusredu'cing the efilciency and flexibility of control of the release of brakes.

. One object of the present invention is to provide a novel brake mechanism of the general type disclosed in the aforementioned Stewart application in which the truck frame supporting springs are not compressed by the braking action of the, mechanism, so as to thereby obviate the difllcuity just described.

Another object of the invention is to provide a novel multi-shoe brake mechanism which is normally carried by the frame of the truclaand which is so arranged as to set up forces in the brake rigging during braking for opposing, to any desired degree, the forces above described which act to move the truck frame downwardly against the frame supporting springs.

Another object of the invention is to provide 5 a brake mechanism for a rotatable member, such as a wheel, which embodies a plurality'of brake elements for engagement with said wheel, and.

a novel-system of levers and links operatively connecting said brake elements for controlling 40 their braking operation.

Another object of the invention is to provide a novel brake mechanism embodying a plurality of brake elements arranged in spaced relation around and adapted to frictionally engage a 15 wheel or other rotatable member to be braked, a system of levers and links operatively connecting said brake elements in serial relation for controlling their operation, and a slack adjuster device connected to one end of said system and automatically operative to compensate for wear of all of said brake elements so as to maintain a predetermined clearance between all of said brake elemenisand said wheel, when the brakes are released.

Other objects and advantages will be apparent Description of parts .As shown in the drawings, the invention is associated with a railway vehicle truck which,

for the purpose of illustration, may comprise the usual truck, frame I and longitudinally spaced wheel and axle assemblies, each of which assemblies may comprise an axle 3 and laterally spaced wheels 3 secured in any desired manner to the axle i for rotation therewith.

The truck frame I comprises side pieces 4 disposed outboard 'of the. wheels 3 and integrally connected together by transversely extending end members I and transoms 3. Adjacent the wheels 3 each side'piece 4 is provided with the usual depending pedestals I between which is slidably mounted a journal box I iournaledon the axle 3. A spring '3 disposed between the pedestals l is interposed between each iournal box 3 and the side pieces 4 of the frame for resiliently supporting said frame from. the axle I. v

A brake rigging constructed in accordance with the invention, and ,to be hereinafter fully described, may be associated with each of the wheels 3 of the truck andail of these brake mechanisms may be identical to each other and operate in the same manner. In view of this and for the sake of simplicity and clarity only one such brake mechanism and the necessary portions of one wheel and axle assembly and of the truck frame are shown in the drawings. v

The novel brake mechanism embodying the invention comprises a plurality of friction brake elements II, II and i3 spaced from each other around the peripheral face of a member to be braked, which as shown in the drawings may be in the form of the wheel 3, said brake elements being arranged for. braking engagement with the annular tread of said wheel.

The brake elements I! and II are arranged at opposite sides oi the tread of wheel 3 in the usual clasp relation and below the horizontal center-' line. of said wheel. The brake element i3 is arranged above the wheel 3 on the vertical centeriine thereof.

Each of the brake elements II, N and i! may be of identical structure comprising a brake shoe 13 provided on the face adjacent the wheel with a surface for frictional engagement therewith. Each of the shoes I3 is carried by a brake head i4 provided on the Side opp0sifc'thc.shoc with spaced parallel flanges ll extending longitudinally of the head. Each of the clasp arranged brake elements II and II is supported directly from the truck frame i by a pair of spaced, parallel arranged hangers ll arranged at one end at opposite sides of the flanges ll of said brake elements and pivotally connected to said flanges by a pin H. The opposite ends of the hangers it connected to each of the clasp brake elements it and H is pivotally connected by a pin II to lugs l3 provided on the side piece 4 of the truck frame, this connection being such with respect to the disposition of said brake elements, that the actionof the iorce of gravity on said elements is to the upper end of 9. depending link 34 the lower adapted to rock said elements away from the wheel 3 to their release positions shown.

Above the side piece 4 of the-truck frame and directly over the tread of wheel 3 is disposed a beam or lever 20 which extends longitudinally of 5 said frame and which is pivotally connected at one end by a pin 2| to a pair of spaced lugs 22 projecting from the frame adjacent the transom 8. The other end of the beam 23 is disposed to work vertically in a pocket 23 which is provided in a member 34 secured to the top of side piece 4 adjacent the truck end member 5. A spring 26 disposed in pocket 23 and supported on the lower end wall of member 24 acts on the end of the beam 33.

The beam 23 extends through the space between the flanges I! on the brake head of the brake element I! located above the wheel and is pivotally connected to said flanges by a pin 3|, the spring 33 acting on the endof beam 20 being provided to normally support said end of said beam and the brake element and to rock said beam in such a direction as to draw the brake element away from the wheel 3 in shooting a release of the brakes after an application, as will be later described.

A spring 32 is interposed between the upper end wall of pocket-33 and lever 23 for securing said lever against undue oscillation which might be caused by the wheel 3 engaging inequalities in -the track rails at rail joints or the like.

The end of beam 23 adjacent the end'of the truck frame is pivotally connected by a pin 33 end of which is pivotally connected by a pin 33 a to the end of a substantially horizontally extending arm of a bell crank 34. The knee of the bell crank 33 is disposed to operate between the flanges I! of the brake head of brake element ll and is pivotally connected to said flanges by the pin IT. The bell crank 3 is provided with a depending arm the end oi which is pivotally connected by a pin 31 to one end of a pair of horizontally extending tie rods 33 which are disposed one at either side of the wheel 3. The opposite ends of the tie rods 33 are connected by a pin 33 to the lower end of a live brake lever 33, this lever intermediate its ends being disposed between the flanges ll of the brake head of the brake element II and being pivotally connected thereto by the pin H. The upper end of this lever extends through a slot 43 in the side piece 4 of the truck frame and is operatively connected by a pin 4! to one end of a horizontally extending link 43 the opposite end of which is plvotally connected by a pin 43 to one end of a lever 44. The opposite end of the lever 44 is connected by a pin 43 to the outer end of a screw 44 of a slack adjuster device 41 which is secured to a bracket 33 rigidly so mounted on the side piece 4 of the truck frame.

A pull rod 43 disposed above and extending I, lengthwise of the side piece 4 is connected at one end by a pin 43 to the lever 44 intermediate its ends. The opposite end of rod 43 is connected by as ton'rod l3. ,j i q The piston rod 35 proiects from a brake 0311- 15 I brake element II in an upwardlydirection tending to lift the truck frame I. In other words, the force; applied to the brake element II which tends to place, the supporting hangers l6 under tension and thus draw the truck frame down against the support spring I is counteracted by the force appl ed through the knee of the bell designed that these counteracting forces will be sufllcientto at least counterbalance the downwardly acting forces, and since the counteracting forces are set up and developed coincident with the build up of braking effort between the brake elements I. and H and wheel 3, the truck frame will remain in the-same position-with respect to the wheel 3 .when the brakes are applied as'occupied immediately prior to the application. As a result, the truck frame support spring 9 will not be compressed and will therefore not influence or sheet in any way the degree of brake application obtained from the pressureof fluid supplied to act in the brake cylinder device I3.

when it is desired to effect a release of the brakes after an application fluid under pressure is vented from the brake cylinder device 36 through pipe 33,. whereupon the release spring 31' acting on the brake cylinder piston %ts to return said piston and thereby the piston rod it back to their release position, shown in the drawin'gs. This operation of the piston rod II acts through the lever 3|, pull rod 43, lever M and link 4! on the live lever 30 to efl'ect rocking movement thereof in a counterclockwise direction. As the live lever 33 is thus rocked it acts to relieve pressure on the brake element l3 and moves the tie rod 33 in a direction toward the right hand, as viewed in the drawings. This operation ofthe tie rod 33 acts throughthe bell crank 33 to relieve pressure of the brake element H on the wheel 3 and also to relieve the force on beam 23 and thereby on the brake element l2.

Further rocking of the live lever 33 then acts through the tie rods 3! and'bell crank 33 to permit the force of gravity acting on the brake ele-' ments II and Ii to rock said elements away from the wheel 3 and back to'their release positions, and also acts. to permit the spring 23 acting on one end of-the beam 20 to rock said beam about its fulcrum pin II in a counterclockwise direction and thus lift the brake element I! out of engage-' ment with the wheel 3 and back to its release position.

It will be noted that since in effecting an apjplication of. the brakes there is no downward movement of the truck frame relative to the wheel 3 and consequent compression of the support spring 0, any reduction in the pressure of fluid on the brake cylinder piston 53 will be promptly reflected through the system of levers and links in a corresponding or proportional reduction in pressure of the brake elements ,IO, II and I! on the wheel 3 so that if desired the brakes on the wheel may be quickly released, gradually or in steps corresponding to the degree of reduction in brake cylinder pressure. In other words, the truck frame is secured against vertical movement relative to the car wheel 3 at the time the brakes or! the wheel are applied, so as to thereby interfere in no way with the degree of application obtained by the pressure of fluid supplied to act in the brake cylinder device and also to provide for; a flexible and accurate control of the release of the brakes on the wheel.

Operation of slack adjuster device It will be noted that the brake elements l2, ll

' and III are connected in serial relation by a systhe brake cylinder device.

When the brake shoes E3 on the several brake elements are new, the screw 46 in the adjuster device is adjusted in the usual manner outwardly of said device a suflicient distance to provide a desired clearance space between the several brake elements, and the tread of wheel-3, when the brake cylinder piston 58 is in izis release position.

With this clearance space between the brake elements and wheel the movement of the brake cylinder piston 88 in efl'ecting an application of the brake will be insufllcient to connect the pressure chamber 53 of the brake cylinder device to the pipe 3! leading to the slack adjuster engine 41, so that the slack adjuster device will not be operated under sucha condition.

As the-brake shoes I! of the severalbrake elements M, H and I! wear away, the travel of the brake cylinder piston 33 required to effect movement of said brake elements into braking engagement with the tread of the wheel increases, and when the wear has increased'to such a degree that said piston moves beyond the connection with pipe 33 in effecting an application of the brakes, fluid under-pressure will flow from the pressure chamber 59 through pipe 55' to the engine 41 of the slack adjuster device. When the brake cylinder piston 33 is returned to its res lease position upon effecting the subsequent release of the brakes, the slack adjuster pipe 35 is connected to the non-pressure chamber 8| in the brake cylinder device, so that fluid under pressure previously supplied to the slack adjuster eng'ine 31 is vented to the atmosphere, whereupon the slack adjuster engine 41 operates to draw the screw 0 in the direction of the engine a predetermined degree thereby changing the location of the fulcrumpin II for the lever 44.

This change in location of the fulcrum pin 43 is reflected, upon the brake cylinder piston 58 ohtaining its release position, in the fulcrum pin 4| for the live lever 33 being located closer to the wheel than before the operation of the slack adjuster device. I

The consequent change in angularity of the live lever 39 when in its release position acts in effect to reduce the distance betweenthe fulcrum pins l1 and as a consequence between the brake elements I 0 and II carried by said pins, and since the force of gravity acting on one of said elements opposes that on the other, both of said elements are therefore stopped, in their release movement away from wheel 3, closer to said wheel than previously.

The mass of the brake elements l0 and II is such that the force of gravity acting thereon during their release djustment to wheell, as just described, is operable to rock the beam 20 against the spring 26 and thus reduce the clearance space between the brake element l2 and wheel 3. Tide slack adjustment of-the brake elements Ill and iii is thus reflectedin a slack adjustment of the brake element I2, the slack adjustment of the three brake elements being thus effected'by the operation of one slack adjuster device.

When the several brake elements again become worn to the extent that the brake cylinder piston in enacting an application of the brakes, moves past the opening to the adjuster pipe 65, the slack adjuster device will again operate as above described to reduce the clearance space between the wheel I and the several brake elements when in their release position. The slack adjuster device will thus continue to operate throughout the life of the several brake elements to maintain a substantially fixed movement of the several brake elements away from the wheel in releasing the brakes, and as a result provide for a substantially constant stroke of the brake cylinder piston in effecting an application of the brakes.

Summary It is important to note that the novel brake mechanism above described provides for accurate and flexible control of the brakes on the truck, due to the fact that its design provides forces in the truck to prevent downward movement of the truck frame which tends to be effected by downwardly acting force's created by forcing the clean arranged brake elements into engagement with the wheel 3 below the horizontal centerline thereof. All of the brake elements are forced into engagement with the wheel by action of the brake cylinder device through a novel system of levers and links which connect the several brake elements together, and which provide for the ready slack adjustment of all of said brake elements by a single slack adjuster device connected to one end of the system.

While one illustrative embodiment of the in-,

vention has been described in detail, it is not the intention to limit its scope to that embodiment or otherwise than by the terms of theappended claims.

Having now described my invention, what I ranged to apply a substantially, horizontal force to said other arm for moving said brake element into braking engagement with said surface.

2. A brake mechanism for a vehicle truck having a rotatable member to be braked provided with an annular braking surface, said mechanism comprising a brake element disposed to frictionally engage said surface, a hanger for said brake element, a bell-crank having a substantially, horizontally extending arm, a pin pivotally connecting said hanger and the knee of said hellcrank to said brake element, avertically movable member connected to said arm, means connected to the other arm of said bell-crank. for actuating said bell-crank, and means for limiting vertical comprising a pair of brake elements arranged in clasp relation at opposite sides of said member for irictionally engaging saidsurface, a hanger connected to each of said brake elements for supporting same, a bell-crank having a substantiab ly, horizontally extending arm and connected at its knee to one of said brake elements, a member movable in a generally vertical direction connected to said arm, a live lever operatively can'- nected to the other brake element and to the other arm of said bell-crank, andmeans for limiting vertical movement of'the vertically movable member for rendering said live lever and bellcrank operable to move said brake elements into braking engagement with said surface.

4. A brake mechanism for a vehicle truck having a. rotatable .member to be braked, provided with an annular braking surface, "said brake mechanism comprising a brake element adapted to frictionally engage saidsuriace at one side of said member, another brake element adapted to fricticnally engage said surface adjacent the ver tical center-line of said member, a bell-crank pivotally connected at its knee to one of said brake elements, means connecting one of the arms of said bell-crank to the other brake element, and means operative on the other arm of said bell-crank for effecting movement of both of said brake elements into braking engagement with said rotatable member.

5. A brake mechanism for a vehicle truck having a rotatable member to be braked provided with an annular braking surface, said mechanism comprising a brake element disposed to frictionally engage said surface on one side of said memher, a second brake element disposed to frictionallY e age said surface at thetop of said member, a lever for operating said second brake element, a. bell-crank connected at its knee to said first brake element and having one arm\ connected to said lever, and means operatively connected to the other arm of said bell-crank for operating same andthereby said lever to move both of said brake elements into braking engagement with said surface.

6. A brake mechanism for a vehicle truck having a rotatable member to be braked provided with an annular braking surface, said mechanism comprising a brake element disposed at one side of said. rotatable member for frlctionally engaging said surface, a second brake element disposed above said rotatable member for irictionally en-- gaging said surface, a lever pivotally connected to said frame and second brake element for controlling the operation thereof,. means for supporting the first named brake element from said frame in braking relation with said rotatable member, a bell-crank pivotally' connected at its knee to said first brake element and havinga substantially, horizontally extending arm, a tension member connecting said arm to the first named lever for controlling its operation, and means for applying a substantially, horizontally acting force to the other arm of said bell-crank for eilecting operation of said bell-crank and lever to move both of said brake elements into braking engagement with said surface. I

7. A brake mechanism for a vehicle truck having a rotatable member to be braked provided with an annular braking surface, said mechanism comprising a brake element disposed above said member and adapted to be moved into frictional engagement with said surface, a beam having a fulcrum connection with said frame and carrying said brake element, means acting on said beam for supporting said brake element out of engagement with said surface, a second brake element disposed at one side of said rotatable member and adapted to be moved into frictional engagement with said surface, a hanger supporting said second brake element from said frame, a bellcrank plvotally connected at its knee to said second brake element and having a substantially, horizontally extending arm, a tension member connecting said beam to said arm, and means for applying a substantially horizontally acting force to the other arm of said bell-crank for operating said bell-crank and beam to effect movement of both of said brake elements into braking engagement with said surface.

8. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said brake mechanism comprising at least three brake elements two of which arearranged at opposite sides of said rotatable member in clasp relation for braking engagement with said surface, while the third is arranged above said rotatable member for braking engagement with said surface, a beam having a fulcrum connection with said frame and connected to said third brake element, a spring acting on said beam for supporting said third brake element from said frame, a hanger for each of said clasp brake elements supporting same from said frame, a bell-crank pivotally connected at its knee to one of said clasp brake elements and having a substantially, horizontally extending arm, a link connecting said arm to said beam, a live-lever pivotally connected to the other clasp arranged brake element, means for actuating said live lever, and means operatively connecting said live lever to the other arm of said bell-crank for effecting operation of said bell-crank and said link and beam to effect movement of all of said brake elements into frictional engagement with said surface.

9. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said brake mechanism comprising at least three brake elements two of which are arranged at opposite sides of said rotatable member in clasp relation for braking engagement with said surface, while the third is arranged above said rotatable member for braking engagement with said surface, a beam having a fulcrum connection with said frame and connected to said third brake element, a hanger for each of said clasp brake elements supporting same from said frame, a bellcrank pivotally connected at its knee to one of said clasp brake elements and having a substantially, horizontally extending arm, a link connecting said arm to said beam, a live lever pivotally connected to the other clasp arranged brake element, means for actuating said live lever, and means operatively connecting said live lever to the other arm of said bell-crank for operating said bell-crank and said link and beam to effect movement of all of said brake elements into frictional engagement with said surface, said hangers and clasp brake elements being so arranged that said clasp brake elements are movable out of engagement with said surface due to the force of gravity, and a spring acting on said beam for dis- 5 engaging said third brake element from said sln'face upon disengagement of said clasp brake elements from said surface.

10. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said mechanism comprising a brake element disposed above said member for frictionally engaging said surface, a beam disposed above said member having a pivotal connection with said frame and carrying said brake element, a pair of brake elements arranged in clasp relation at opposite sides of said member, a hanger for each of said clasp brake elements, a bell-crank having its knee connected to one of said clasp brake elements and 20 having a substantially horizontally disposed arm,

a link connecting said arm and beam, a live brake lever operatively connected to the other clasp brake element, a tie rod connecting said live lever to the other arm of said bell-crank, a brake 25 cylinder device operatively connected to said live lever for controlling operation thereof and of said bell-crank and beam to effect movement of all of said brake elements into and out of braking engagement with said rotatable member, and 30 means operative on said beam to disengage the first named brake element from said rotatable member upon disengagement of said clasp brake elements therefrom.

11. A brake mechanism for a vehicle truck 85 having a truck frame and a rotatable member to be braked provided with an annular braking surface, said mechanism comprising at least three brake elements arranged in spaced relation around said surface, two f said brake elements 40 being rigidly supported from said truck frame against vertical movement relative to the frame, a system of levers and links operatively connecting said brake elements in serial relation, one end of said system having a fulcrum connection with said frame, actuating means for applying force to the other end of said system for operating said system to effect movement of all of said brake elements into braking engagement with said surface, and means securing said brake elements against movement with said rotatable member.

12. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said mechanism comprising at least three brake elements arranged in spaced relation around said surface, two of said brake elements being rigidly supported from said truck frame against vertical movement relative to the frame, a system of levers and links connected serially with each other and operatively connecting said brake elements in serial relation, one end of said system having a fulcrum connection with said frame and the other end of said system terminating in a lever having a fulcrum connection with one of said brake elements, and means for applying force to said lever for operating said system to effect movement of all of said brake elements into braking engagement with said surface.

13. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said brake mechanism comprising at least three brake elements for engaging said surface, two of said elements being arranged .at opposite sides oi. said member in clasp relation and the third brake element being disposed above said member, a horizontally extending lever having a fulcrum connection with said frame and connected to said third brake element for controlling its operation, a live brake lever connected to one of said clasp arranged brake elements for controlling its operation, a bell-crank pivotally connected at its knee to the other clasp arranged brake element and. having one arm operatively connected to said horizontally extending lever and the other arm operatively connected to said live brake lever, and means for actuating said live brake lever and thereby said bell-crank and horizontally extending lever for effecting movement of all of said brake elements into braking engagement with said surface.

14. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said brake mechanism comprising at least three brake elements arranged in spaced relation around said surface for frictional braking engagement therewith, a system of levers and links operatively connecting said brake elements in serial relation with respect to each other, one end of said system having a fixed fulcrum connection with said frame, a slack adjuster device comprising a slack take-up element providing a fulcrum for the other end of said system, and a brake cylinder device operatively connected to said system for controlling theoperation of said brake elements. I

15. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said brake mechanism comprising at least three brake elements arranged in spaced relation around said surface for frictional braking engagement therewith, a system of levers and links operatively connecting said brake elements in serial relation with respect to each other, one end of said system having a fixed fulcrum connection withsaid frame, the other end of said system terminating in a lever, a slack adjuster device comprising a. slack take-up element providing an adjustable fulcrum for the last named lever, and a brake cylinder device operatively connected to said last named lever for least three brake elements arranged in spaced relation around said surface for frictional braking engagement therewith, a system of levers and links operatively connecting said brake elements in serial relation with respect to each other, a slack adjuster device comprising a slack take-up element providing a fulcrum for one end of said system, and a brake cylinder device operatively connected to said system for control= ling the operation of'said brake elements.

17. A brake mechanism for a vehicle truck having a truck frame and a rotatable member to be braked provided with an annular braking surface, said brake mechanism comprising at least three brake elements for engaging said surface, .two of said elements being arranged at opposite'sides of said member in clasp relation and the third brake element being disposed above said member, a horizontallyextending lever having a fulcrum connection with said frame and connected to said third brake element for controlling its operation, a live brake lever connected engagement with said rotatable member, a. spring 

